The invention generally relates to a gas lift valve assembly.
For purposes of communicating well fluid to a surface of a well, the well may include a production tubing. More specifically, the production tubing typically extends downhole into a wellbore of the well for purposes of communicating well fluid from one or more subterranean formations through a central passageway of the production tubing to the well's surface. Due to its weight, the column of well fluid that is present in the production tubing may suppress the rate at which the well fluid is produced from the formation. More specifically, the column of well fluid inside the production tubing exerts a hydrostatic pressure that increases with well depth. Thus, near a particular producing formation, the hydrostatic pressure may be significant enough to substantially slow down the rate at which the well fluid is produced from the formation.
For purposes of reducing the hydrostatic pressure and thus, enhancing the rate at which fluid is produced, an artificial-lift technique may be employed. One such technique involves injecting gas into the production tubing to displace some of the well fluid in the tubing with lighter gas. The displacement of the well fluid with the lighter gas reduces the hydrostatic pressure inside the production tubing and allows reservoir fluids to enter the wellbore at a higher flow rate. The gas to be injected into the production tubing typically is conveyed downhole via the annulus (the annular space surrounding the production tubing) and enters the production tubing through one or more gas lift valves.
As an example, FIG. 1 depicts a gas lift system 10 that includes a production tubing 14 that extends into a wellbore. For purposes of gas injection, the system 10 includes a gas compressor 12 that is located at the surface of the well to pressurize gas that is communicated to an annulus 15 of the well. To control the communication of gas between the annulus 15 and a central passageway 17 of the production tubing 14, the system 10 may include several side pocket gas lift mandrels 16 (gas lift mandrels 16a, 16b and 16c, depicted as examples). Each of the gas lift mandrels 16 includes an associated gas lift valve 18 (gas lift valves 18a, 18b and 18c, depicted as examples) for purposes of establishing one way fluid communication from the annulus 15 to the central passageway 17. Near the surface of the well, one or more of the gas lift valves 18 may be unloading valves. An unloading gas lift valve opens when the annulus pressure exceeds the production tubing pressure by a certain threshold, a feature that aids in pressurizing the annulus below the valve before the valve opens. Other gas lift valves 18, typically located farther below the surface of the well, may not having an opening pressure threshold.
The gas lift valve 18 typically contains a check valve element that opens to allow fluid flow from the annulus into the production tubing and closes when the fluid would otherwise flow in the opposite direction. For example, the production tubing 14 may be pressurized for purposes of setting a packer, actuating a tool, performing a pressure test, etc. Thus, when the pressure in the production tubing 14 exceeds the annulus pressure, the valve element is closed to ideally form a seal to prevent any flow from the tubing 14 to the annulus 15. However, it is possible that this seal may leak, and if leakage does occur, well operations that rely on production tubing pressure may not be able to be completed or performed. Thus, an intervention may be needed, which may be costly, especially for a subsea well.
Thus, there exists a continuing need for better ways to prevent a gas lift valve from leaking.